When animals, especially dogs and cats, are kept as pets in dwellings intended primarily for human habitation means must be provided for them to relieve themselves. Traditionally said means has been a box or pan filled with a quantity of absorbent granular material (also known as litter) such as clay.
This use of absorbent granular materials as a receptacle for animal excreta is intended to serve three distinct needs. First, the material acts as a medium in which the pets, particularly cats, can satisfy their natural instinct to dig. Second, the material is intended to absorb urine. Third, the material serves as a receptacle for solid excreta (i.e., feces).
Currently employed absorbent granular materials perform adequately at satisfying the first need. However, current products are extremely poor at the latter two needs. The absorptive capacity of clay is extremely low, usually less than one gram of liquid absorbed per gram of litter. Furthermore, the absorptive process causes the granular material to clump, rendering it unacceptable as a digging medium. This clumping, in addition to the accumulation of feces, necessitates frequent and messy changes of the litter.
Several attempts have been made to eliminate the problem inherent to the system as described. U.S. Pat. No. 4,774,907 issued to Yananton on Oct. 4, 1988 teaches the use of a liquid absorbent pad in conjunction with the clay granules in an attempt to extend the life of the litter. The problem with this solution is that urine must first flow through and potentially be absorbed by the clay granules before it is absorbed by the underlying pad. In this case the pad does not necessarily extend the life of the litter but rather absorbs the "overflow" urine that passes through the urine-soaked o litter. Furthermore, the absorbent pad disclosed in U.S. Pat. No. 4,774,907 does nothing to address the issue of solid waste.
The problem of handling solid waste has been considered in several prior art references. U.S. Pat. No. 4,817,560 issued to Prince et al. on Apr. 4, 1989 and U.S. Pat. No. 4,096,827 issued to Cotter on June 27, 1978 describe reusable filters which are intended to remove feces from the absorbent granular material (i.e. litter). Similarly, U.S. Pat. No. 3,809,013 issued to Rigney on May 7, 1974 and U.S. Pat. No. 4,312,295 issued to Harrington on June 26, 1982 describe disposable filtering mechanisms.
However, none of the aforementioned patents address the inherent problem associated with filtering absorbent litter which has formed clumps due to the absorption of urine. These clumps adversely affect the filtering operation, and are sometimes so large that they impede the flow of "unused" litter through the filtering screen. Furthermore, these clumps often break apart as they are being filtered, thereby releasing an intense and offensive odor.